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The Use of Upright Drainage on Diuretic Renography to Predict Clinical Outcomes in Prenatal Hydronephrosis
Michael Ernst, MD1, Bayan Shalash, BS2, Megan Stout, MD2, Lindsey Asti, Phd MPH3, Daryl McLeod, MD MPH1.
1Nationwide Children's Hospital, Columbus, OH, USA, 2Ohio State University, Columbus, OH, USA, 3Center for Surgical Outcomes Research and Kidney Urinary Tract Research Center, Columbus, OH, USA.

BACKGROUND: In infants with prenatal hydronephrosis and concern for ureteropelvic junction (UPJ) anomaly, 99mTc-mercaptoacetyltriglycine diuretic renography (DR) is used to measure differential renal function and drainage half time, to help identify which children will ultimately benefit from surgery. Unfortunately, it is often necessary to repeat this invasive testing to evaluate for changes over time prior to making a surgical decision. Clearance while upright (CUP) is another metric often calculated in those with abnormal DR, however the clinical significance of this measurement is poorly understood. The purpose of this study was to determine whether CUP, alone or in combination with T1/2 on initial DR predicted eventual surgical correction. correction.
METHODS: Infants younger than one year old with isolated unilateral hydronephrosis that underwent a DR scan between 2009 and 2021 were identified retrospectively at a single institution. Those with other structural anomalies, only one DR scan prior to surgery, or less than one year of follow-up without surgery were excluded from the study. Initial and follow-up differential function, T1/2, and CUP were extracted. Pearson chi-square or Fisher's exact tests were used to compare categorical variables and Wilcoxon rank sum tests were used for continuous variables. Receiver operating characteristic (ROC) curves were generated using logistic regression models with surgery as the outcome to evaluate the area under the curve (AUC) for T1/2, upright drainage percent, and both factors together. The Youden Index was used to determine the optimal cut-point for each ROC curve. Using the optimal cut-point, we calculated the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) .RESULTS: A total of 65 patients with congenital hydronephrosis and presumed UPJ anomaly met inclusion criteria. Of these, 33 (51%) had pyeloplasty and 32 (49%) resolved without surgery, with no demographic differences between the groups. The median T1/2 at initial DR for those who underwent pyeloplasty was 44.5 minutes (interquartile range (IQR): 25-100) vs. 21.2 minutes (IQR: 16-31) for patients observed (p=0.001). Similarly, for CUP percent the median for those who underwent pyeloplasty was 19.6% (IQR: 11.0-29) vs. 42% (IQR: 26-59) for patients observed (p<0.001). Separate ROC curves for T1/2 and CUP, and with both variables together demonstrated no significant differences in the AUC. The optimal cut-point for T1/2 was 28.1 minutes, with a sensitivity of 70%, specificity of 75%, and PPV of 74%. In comparison, the optimal cut-point for CUP was 22.4%, which was less sensitive (61%), but more specific (97%) and had a higher PPV (95%) than the T1/2 cut-point in predicting surgery.
CONCLUSIONS: Compared to T1/2, CUP provides a higher specificity and PPV for whether an individual with congenital hydronephrosis with suspected UPJ anomaly is likely to need surgical intervention. With this information, providers can counsel families that if their child's CUP is <22.4% there is a high likelihood surgery will ultimately be recommended and may consider closer surveillance. Neither T1/2 nor CUP provided suitable sensitivity or NPV on initial DR to accurately identify children who do not need surgery.


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